The backlight is controlled independently from the display driver, with one exception: If the registry settings for backlight GPIO and display GPIO are identical, a change of the backlight will also change the state of the display driver accordingly.
Please refer to Display driver registry settings for details.

By default, the backlight is turned off after a timeout that starts whenever there is no user activity on the system. It is automatically turned on as soon as there is any user activity detected.

The backlight timeout can be controlled manually from the control panel:

Control Panel -> Display

These settings are stored in the registry at key name:

[HKCU\ControlPanel\Backlight]ACTimeout=dword:0x00000258 ;Time[seconds] before Backlight is turned off when on external powerBatteryTimeout=dword:0x00000258 ;Time[seconds] before Backlight is turned off when on battery power

.

In order to completely avoid the backlight from turning off, the following registry settings need to be added:

; never turn off backlight[HKCU\ControlPanel\Backlight]UseExt=dword:0x00000000 ; 0: don't switch off backlight when on external power
UseBattery =dword:0x00000000 ; 0: don't switch off backlight when on battery power

.

Note: On IMX6 image this feature is supported only on release 1.3b4 or newer and is disabled by default, set "UseExt" and "UseBattery" entries to 1 to enable it.

You can use the ExtEscape() function to control the backlight from your application, overriding the automatic user activity / timeout detection.
The code below shows the basic structure of a call to ExtEscape().
The function sets the backlight status to the value new_backlight, and returns the backlight status before applying the change in old_backlight.